stuck in question loop (Is b positive or negative?)

There are three bugs in Maxima here:

1) It shouldn't be asking about the sign of b at all.

2) It should be possible to escape from the questions using control-G

3) plot2d doesn't give an error message for an input of the wrong kind
(an equation rather than an expression).

But there are also two user errors:

1) plot2d expects an *expression*, not an *equation*, e.g. plot2d(3^x,[x,-5,5])

2) the value of b is undefined, so Maxima can't plot values for b^x.

Hope this helps,

              -s

---------------------------------------------
a:y=b^x;

plot2d(a,[x,-5,5]);

To which it asks:
> Is  b  positive or negative?

Can't get past that point.  Have tried typing p, pos, positive.
No matter how I reply, it does not take the answer, it just
repeats the question.